1. Field of the Invention
This invention relates in general to domestic appliances powered by an electronically commutated motor (ECM) a method of operating an ECM and more particularly to a method of controlling the speed or torque of an ECM.
The invention further relates to control circuits for ECMs suited to fabrication in solid state electronic form to a large degree utilizing monolithic integrated circuitry, and to an ECM powered variable speed fan incorporating such control circuitry.
2. Description of the Prior Art
Control circuits for electronically commutated motors have hitherto been fabricated using discrete electronic components, and yet the desirability of fabricating such control circuits in solid state electronic form, to a large degree utilizing monolithic integrated circuitry, is widely honored in discussions among electrical industry spokesmen if not by an equally wide presence of products incorporating such monolithic integrated circuitry in the actual market place.
The electronically commutated motors for which such control circuitry would have application is exemplified by those ECMs disclosed in U.S. Pat. Nos. 4,005,347 and 4,169,990 to David M. Erdman, and U.S. Pat. No. 4,162,435 to Floyd H. Wright. These motors are characterized by having a multistage winding assembly, and a magnetic assembly, the two arranged for mutual relative rotation, the motor in a given state of a multistate energization sequence, having an unenergized winding stage in which an induced back emf appears, which when integrated over time to a predetermined value indicates the instant at which the mutual relative angular position has been attained suitable for commutation to the next state. In the most common examples, the multistage winding assembly is stationary, with the magnetic assembly arranged within the winding assembly, and arranged to rotate with respect to the immediate environment by means of bearings attached to a frame, mechanically common with the winding assembly. The mechanically opposite arrangement in which the winding assembly rotates within the magnetic assembly is less common, but makes many of the same requirements of the control circuitry, and in general the control circuitry has equal application to such motors. In addition, the more common, magnetic assembly in such motors is a permanent magnetic assembly. However, an arrangement in which the magnetic assembly is electromagnetic makes many of the same requirements of the control circuitry, and in general, the control circuitry has equal application to such motors.
The common requirements of the control circuitry for electronically commutated motors, may be divided into four categories, which in a sense, place differing requirements upon their fabrication. The appliance is installed in the house, and controls located when practical in the appliance, and when not practical, located at wall locations convenient to the user. In the practical case of a combined ceiling fan, lighting fixture, which is the practical product exemplified herein, the "fan" includes a motor, a light and user operated controls for the same. The controls are both integral with the lighting fixture and remote. The remote control may be located upon a convenient wall location and it may embody largely duplicate user operated controls. The usual functions of the user operated controls include turning on or turning off the fan or light, regulating the intensity of the light, regulating the speed of rotation, or direction of rotation of the fan.
The user operated controls, particularly those on the wall controls, are themselves constructed similarly to other wiring devices used in the home, and they are interconnected by electrical cable typical of the customary 110 AC house wiring. In general, the requirement placed upon such "control systems" is that the interconnections be minimal, and if possible not require additional special wiring. Ideally, the wiring installation would permit complete communication within the "control systems" by the minimum two wire cable. Ideally, the user operated control circuitry exemplified herein should require no more than two wires between the wall control, the fixture, and the house wiring for minimum installation expense. In this category, the control circuit is fabricated in the form typical of house wiring systems.
A second category of electrical control circuit fabrication is utilized within the enclosure of the ceiling fixture or of the wall control. This usually is "point to point" wiring, and the electrical connections are made with mechanical bonds, including solder, rivets, or electrical terminals. Here, the stress is often upon compactness, and ease of on-site assembly.
A third category of electrical control circuit fabrication, which is often practiced in the fixture itself or in the wall control, is that which is usually performed in the factory, and which is called "printed circuit board" (PCB) wiring. This wiring is of moderate density, and allows for ampere level currents, voltages in excess of the customary house level voltages (120-240, etc.), and heat dissipation levels comparable to the needs of the customary home appliances. This wiring is used to interconnect--by a factory process, discrete electronic components, such as resistors, capacitors, inductors, discrete solid state devices, such as transistors, diodes, diacs, triacs, SCRs, etc. on the printed circuit board.
When the control application of the control circuitry is as complicated as the provision of electronic commutation of an ECM motor and the imposition of user operated controls, and automatic protection functions incidental to user operated controls, then the complexity of the control function required of the control circuitry tends to transcend the practical limits of fabrication by the assembly of discrete electrical components upon a printed circuit board. In the printed circuit mode of fabrication for such control circuitry, the volume weight, and costs of printed circuit fabrication are greater by a factor of at least a hundred, and often by a factor of a thousand times the comparable measure of a circuit of monolithic integrated circuit fabrication of like complexity.
The thurst of these practical considerations upon control circuit fabrication is to perform all of the control functions that can be performed, taking into account the limitations on allowable current levels, voltage levels and power dissipations, with monolithic integrated circuitry.
Present day limitations upon the application of integrated circuitry are less restrictive than some time ago, and more restrictive than one would expect some time in the future. In general, circuitry complexity required for the control function herein contemplated can be handled with MSI (Medium Scale Integration) or LSI (Large Scale Integration). In the usual case, the component count of the motor control system is on the order of 10.sup.2 to 10.sup.3.
The current, voltage and power dissipations ordinarily dictate special interfacing circuits between the monolithic integrated circuit and the user operated controls, the motor, the light and the power mains. In general, this dictates that voltages applied to the IC not exceed the voltage rating of the integrated circuit process, typically from 5 to 40 volts, that currents should not exceed tens of milliamperes and that power dissipation not exceed 100s of milliwatts. Because of voltage limitations, it is necessary to use voltage dividers coupled to the winding stages of the motors to reduce the back emf sensed on the winding stages to several volts (e.g. about 3 volts) before application to the integrated circuit. Similarly, the control of power to the winding stages of the motor requires current and power dissipation levels that can only be performed by discrete solid state switches. The integrated circuit, accordingly, has terminal pads supplied by internal drivers, with the power to control either directly or through additional buffers, the solid state power switches energizing the winding stages of the motor. A similar practical problem relates to the non-integrable components, which are primarily large capacitors, inductors, and the user operated controls. These may usually be coupled to the pads of the monolithic integrated circuit with no other transition than the terminal pads of the integrated circuit and a demountable 16 pin connection on the printed circuit board.
There is a need to use a standard package with ICs in order to keep the cost minimum. This is typically 16 pins. There is also a need to keep outboard of the IC, components which control parameters which may change from product to product such as the inertia of the fan blades. In other words, the IC must be able to adapt to expected changes and must use a standard low cost package. Some components which could be integrated are sometimes not put in the IC for these good engineering reasons.
To date, "maximally" monolithically integrated control circuits for electronically commutated motors are not in common use in the market place.